poggio@apple.com (Andy Poggio) (02/28/90)
CD Summary Introduction
As requested by many people, I will post this CD Summary over the next
several days in five parts of which this is the first. I received
requests from rec.audio, comp.ivideodisc, and comp.graphics -- so I will
post it to all these groups. I'm not sure that it is appropriate for
comp.graphics but I DID receive multiple requests to post it there.
The summary is somewhat technical but more important it is factual: I
wrote it after reading the original CD standards documents available from
Sony or Philips to CD licensees. If you are interested in the standards
documents, you need to contact them directly -- sorry, I don't have a
specific contact or phone number.
I do work for Apple but this summary contains a minimum of Apple
references. I hope everyone agrees that the result is in keeping with net
policy on the matter.
--andy
CD Summary Part 1
CD-ROM Technical Summary
From Plastic Pits to "Fantasia"
Andy Poggio
March, 1988
Abstract
This summary describes how information is encoded on Compact Disc (CD)
beginning with the physical pits and going up through higher levels of
data encoding to the structured multimedia information that is possible
with programs like HyperCard. This discussion is much broader than any
single standards document, e.g. the CD-Audio Red Book, while omitting much
of the detail needed only by drive manufacturers.
Salient Characteristics
1. High information density -- With the density achievable using optical
encoding, the CD can contain some 540 megabytes of data on a disc less
than five inches in diameter.
2. Low unit cost -- Because CDs are manufactured by a well-developed
process similar to that used to stamp out LP records, unit cost in large
quantities is less than two dollars.
3. Read only medium -- CD-ROM is read only; it cannot be written on or
erased. It is an electronic publishing, distribution, and access medium;
it cannot replace magnetic disks.
4. Modest random access performance -- Due to optical read head mass and
data encoding methods, random access ("seek time") performance of CD is
better than floppies but not as good as magnetic hard disks.
5. Robust, removable medium -- The CD itself is comprised mostly of, and
completely coated by, durable plastic. This fact and the data encoding
method allow the CD to be resistant to scratches and other handling
damage. Media lifetime is expected to be long, well beyond that of
magnetic media such as tape. In addition, the optical servo scanning
mechanism allows CDs to be removed from their drives.
6. Multimedia storage -- Because all CD data is stored digitally, it is
inherently multimedia in that it can store text, images, graphics, sound,
and any other information expressed in digital form. Its only limit in
this area is the rate at which data can be read from the disc, currently
about 150 KBytes/second. This is sufficient for all but uncompressed,
full motion color video.